Saturday, July 16, 2011

Ok, Replibot is back online. It has been over a year since the last post. Work and moving into a new fixer upper has taken all my time but I’m starting to get back to some normalcy.

I had a question from a friend that I’ve been wanting to get to and today I had some time :

“I've watched several clips about these printers and still don't understand how they measure and then 'print' allowing space for an object (axle/shaft/etc.) to turn in or a key way in which something can move back and forth in etc. If you can explain I would really appreciate.”

So I have to say that I am clearing out a few cobwebs that developed over the last year so I hope others will speak up where correction is needed.

When I have an idea for a design the first thing I do is to capture it using pencil and paper. Actually I use a black ink pen and a blank piece of paper. Sometimes it’s graph paper but I really don’t like following lines until I need to.

Then I get the idea into the computer. What tool I use depends on what I am trying to achieve and my mood at the time. My favorites are Google Sketchup (http://sketchup.google.com/) and Open Scad (http://www.openscad.org/). There are others I use but these take care of 90% of what I need. Both are FreeWare.

The design then needs to be exported so it can be processed by another program. The most preferred format is the *.STL. I think STL stands for Stereo Lithography and that’s all I know about it.

At this point the design is still not at the point where you can click print. The STL need to be processed by a G-Code generator. The only one I have ever used is Skeinforge.

Skeinforge is an remarkable piece of software. It is python scripting that knows everything about the printer and the material you are using. It knows how far the print head travels for each step of the motor, how big the nozzle is, speed, width ,temperature - (and the list goes on). It knows because you or someone else told it by filling in a BUNCH of attributes about your printer and the material being melted to build the printed part.

For 3D printers, it’s using this information to slice the design into layers. Each layer is the vertical resolution of the 3D printer. You can think of each layer as a separate drawing that is stacked one on top the other like a stack of cards. One card by itself is really almost 2D but a deck of cards has a definite 3rd dimension. Vertical holes are made by not extruding material in the area where the holes exist. That area is avoided by the printhead for each of the layers penetrated by that hole. The same reasoning applies to horizontal holes but is a bit trickier because of gravity. I have clean horizontal holes out with a drill bit because of deformity due to gravity. So holes that are critical should be placed vertically if possible by aligning the part that way. Also overhangs can only be made at a certain slope. Skeinforge takes care of a lot of stuff to help with this.

It’s not only 3D printers that Skeinforge is good for. Any tool where the path is robotically controlled could use Skeinforge to generate G-Code for the design.

Another tool I use is Pleasant3D which is a STL and G-Code view for Mac. You can orient and locate STL files and see the tool path of G-code files. Pretty colors are the G-Code and grey is the STL.